Method of making plywood



Patented Oct. 18, 1932 UNITED. STATES PATENT OFFICE THEODORE WILLIAMSDIKE, OF NEW WESTMINSTER, BRITISH COLUMBIA, CANADA, ASSIGNOR, BY MESNE.ASSIGNMENTS, TO LAMINATING PATENTS CORPORATION, OF SEATTLE, WASHINGTON,A CORPORATION OF DELAWARE METHOD OF MAKING PLYWOOD No Drawing.Application filed January 29, 1929, Serial No. 335,998. Renewed March10, 1931.

My invention relates to the art of glluing, and more particularlytoproceduresa apted for the formation of plywood and the like andinvolvingthe application of the adhesive in discrete-particle form,such, for example, as a dry powder or a suspension of discrete-particlesin a fluid.

In general, the object of the invention is the provision of a procedurewhereby improved'results may be obtained and a better and cheaperproduct provided.

Other objects will in part be obvious and will in part appear.hereinafter.

By plywood I mean to include all structures embodying at least one plyor lamination of Wood, whose thickness is not greater than can be causedto adhere to the balance of the structure under the conditions of myprocess, for instance, of sufficient thinness so that the heat of a hotpress can penetrate to the glue line sufficiently to cause setting ofthe adhesive, and I include in the term plywood, also the termveneering. In this connection it is to be understood that the term woodis intended to include not only the natural product, but-also artificialwoods having a porous structure similar to natural wood, such, forexample, as pulp board. 1

By water resistant plywood'I mean plywood whose glue or adhesive binderis of such a nature that subjection of the plywood to twenty-four hourssoaking in cold water does not cause separation of the plies.

In the manufacture of plywood or gluing of wood in general the formationof a glue bond depends upon bringing the glue into a plastic conditionin place between the plies to be joined, so that good contact isobtained between the glue substance and' -the surfaces of the woodWhenpressure is applied to the assembly and then setting the glue inplace so that it forms a strong transversely (i. e. perpendicular to thefaces) substantialy continuous film joining the two wood surfaces, towhich film the penetrating elements are attached. The surfaces of woodprepared for joining as seen under a microscope are very rough andperforated with numerous openings or pores, some of which her ofopenings or pores.

extend for a relatively great distance into the wood.

Whether the bond between glue and wood is formed by true adhesion, i.e., specific adhesion, between the glue substance and the woodsubstance, or whether the bond is mechanical, that is, due to the gluepenetrating into the numerous irregularities of the surface of the Woodand on being hardened in place, producing a bond due to a keying effectas of plaster on lath, it is obvious that other things being equal, thegreater the contact the glue has with the surface of the wood, thebetter will be the bond formed.

However, if the glue penetrates too deeply into the pores and otheropeningsin the wood, the supply of glue between the surfaces to bejoined may be so depleted that a strong transversely continuous filmjoining the two surfaces cannot be formed, and aninferior bond willresult. This condition is known as a starved joint. When two pieces ofwood are joined with an adhesive, it will be obvious that there must bea substantially continuous film of adhesive between the two pieces, in atransverse direction. It may be that penetration to a certain extent isnecessary beyond the boundaries of this continuous film, but the firstrequisite is the transversely'continuous film; this is the foundation ofadhesion.

The extent to which the glue penetrates into the wood depends partlyupon the nature of the wood, which varies as to size and num- It dependsalso upon the effective pressure exerted upon the glue and also upon thefluidity or mobility of the glue while it is under pressure. By fluidityof adhesive I mean those properties of a material which regulate theflow of the material under a given pressure and through a given sizedorifice. No matter whether the flow depends on the size of discreteparticles suspended or enmeshed in a liquid medium, or whether itdepends on viscosity of a true liquid, I include both of these or anyother factors which may influence flow, including also plasticity of adiscrete particle or collection of particles. I recognize that in caseof a suspension, if the orifice is smaller than the swollen particlesize, then the rate of flow many of the pores are intersected by thefaces so that they present openings on the faces into which glue canreadily penetrate if it is sufficiently fluid. There are also otheropenings (rays) in some woods in a direction perpen dicular' to thefaces. The wood tells themselves are much smaller but do permitpenetration by the more fluid glues. Besides these openings natural tothe wood, there are the checks or cracks that are formed inthe cuttingof the veneer as well as other irreguarities of surface. Thuswithwood'there are abundant opportunities for a fluid to escape from thesurface.

The cold press method of gluing using dry veneer is the most commonlyused at present. In this method the plies are assembledin a pile orrack, the cores having been previously passed through a glue spreaderwhich coats both surfaces of the core with a film of liquid glue. Afterthe pile is assembled it is put under pressure and held thus until theglue bond is formed. y

There is also in use a method of hot. pressin g using either dry or wetveneer. In these methods the plates of the press are heated and only oneor at most a very few panels are inserted between the hot plates. Thespreadin g of the glue is in general the same as with I the cold pressmethod.

In the cold press method it has been the custom to disperse the gluesubstance in an aqueous medium. By dispersion I mean producing acollodial system in which dilution can be carried to a high degreewithout apparent loss of homogeneity in the system. I also distinguishbetween suspensions and dispersions, as a matter of particle size.Dispersions have particles much smaller than suspensions.

\Vhen water is mixed with a glue substance to form a dispersion thefluidity of the dispersion is increased if more water is added. In mostinstances, as with casein, soya bean and most starch glues, the gluesubstance is dispersed'by the use of alkaline reagents. Animal glue andsome modified starches are dispersed with water alone. Blood albumen isdispersed in cold water.

The making of a glue, using the dry glue substance, water and whateverchemical reagents are necessary, requires a high degree of skill, bothon the part of-the manufacturer of the dry glue substance, as well asthe operator who makes the dispersion of the dry glue in the water, andwho often must add further chemical reagents.

'it can be used.

wet glue must be of proper'consistencytopick up 'on'thespreaderrolls-and in turn to leave the rol'l'sfor the wood'plywhenitispassed through the rolls, so as to form a uniform film' of'glueon the face of the ply of just the required amount. The wet glue must beof such a" consistency" that it' will not be wiped ofl the faceof theplies accidentally in handling. The 'wet gluemust not change materiallyin either consistency or. viscosity with time. That is it must remainas'nea'rly as possible inits original state foranumber of hours until abatch of glue can be used.

Besides these factors which have nothing to do with, adhesiondirectly,"the're are also the very important factors which influence therelation of adhesion to the age-of the wet and also retain its adhesiyeproperties until It will be seen therefore that there are manyfactors'which must be'reckoned with 'in'm'akglue. That is, the glue mustremainworkable ing'aglue, besides the primary factor of'adhesion. Infact,oftentimes adhesion must'be sacrificed to a. certainextent,"inorder that the secondary) factors be correct to make aworkable glue. 1

, When in the common process of gluing, a

dispersed glue is" applied to'dry-yeneen-the dry wood quickly absorbssome of'thewater from the glue, thus greatly'de'creasing the fluidity ofthe film or layerof glue. This decrease in fluidity is necessary to theformation of a good bond,-'foritprevents the glue from penetrating intothe wood too much and thus giving a starved-joint. If pressure isapplied a few seconds after the glue is applied, and thusbefore therehas been time" enough for waterto pass'fromthe glue to the wood tothicken the glue, veryinferior adhesion will be obtained and it canbe'shown my microscopic examination that theglue has penetrateddeeply'into the wood. On the other hand, if too long a time is allowed.to elapse between the time when the wet adhesive is applied to thesurface of thewood and the time when pressure is applied, then duringthis time the glue may have dried out too much by reason of the water ofthe glue having soaked into the wood and whenthepressure is applied theglue is not fluid enough to make a proper bond. M a

Since the laying up ofapile ofpanels requires from lOto 30 minutes, thelength of time which elapses between spreading'of glue and applicationof pressure, i. e. the time of assembly varies from perhaps a minute Cal' and expensive to handle. I drying the veneer v in separate pieces'lseliminated by using the or two for the lastipanelsspread to over 30minutes for the first panelsspreadl lence" in this process: theconsistency of the \vet glue must always be a, compromise between"thatbesta'dapted for the minimum and maxim m times of assembly respectivelyand like; an compromises it. cannot suit the. extremes conditions exist,relative to the change in Hence thefirst and last paneig'laid are ofinferior quality to those in the, middle of the rack. l

If the glue is fluid enough sothatit can stand aitime-of jassemblyfof 30minutesand still not dr out too: muchbefore pressure is applied, it isso thin that the, last panels l'ai d,

. with time ofassembly of a few minutes, have starved joints. it is madethick, enough to escape starved" Joints on the short time of I assembly,then the ffirst panels laid will have dried out too m'uchivvhenjpressureisapplied.

Thus the cold p'ress "dry" veneer method with Wet; glueis at bes scompromise and has n 1 3. 's v d- The hotpress; method using dry veneerhas the disadvantages requiring the drying out w of theveneer'in aseparate operation, as well i as the disadvantages connected with theprep aration and properties of the glue as regards foam, variationofviscosity wi'thage, and instability of the Wet'glue previouslydiscussed. It employst-he maximum amount of equipment, that'is,'i t usesboth a'drier and hot presses, which renders it soexpensivethat it V isvery littleiised in the United States, This process employs bothdispersedfandjeh lied glues. The dispersed glues are attend edfwiththeir inherent disadvantages as, discussed under 'cold'p'roc'ess. The jelliedglues necessarily have a high moisture content, and

many of themjhave-thefurtherfdisadvantage of losing their jellystructure and 'liquefying' When heat is applied. (A jellied' glue is onethat has been first dispersed 'andthen has some chemical reagent.)

veneer is dried it tends to check or" crack,

causing a serious loss. 'Also the pieces tend 'to curl'and distortrendering them difficult "This; disadvantage of hot press as a drier,When the assembled panel, that is, the piec'es'ot veneer Withadhesiveinterposed,'is dried in the hot press,

there is less opportunity for the veneer to check, crack'ordistort.-Als0 the-handling of the-pieces is less, with attendant econ omy,"sincetwo-'handlings of the pieces into and out'of the drier ar'e eliminated.

'It'has been attempted in the past to realize theadvantages 0f the hotpress Withv green been chan ed to a jelly-like mass by'heat or' of theveneer and its escape through the Veneer. In gluing panels from greenveneer by the hotpress method,it is desired to 'form the glue bond anddry the panel out in one operationand it is in fact necessary to re-'movemostof the moisture from the panel in order to set the glue bond.

In this process of gluing a difierent set of Water istaken from the gluesubstance, and

itsfluijdityis not decreased. On the contrary when heat and pressure isapplied the Water in the Wood tends to dilutethe glue substance thusincreasing its fluidity. Hence if it is atitemptedto' glue Wet'ven'eerby the hot press v metho d with the common dispersed glues inherentdlflicultles which have hitherto not v I trates'in'to the wood to suchan extent that no bon d is obtaine'd'because the glue penethere ispractically none left between'the surfaces to be'joined.v

xgreatly thicken or gel the glue before apply ingit to th'elveneer, bythe use'of such coagulating agents'as heat or formalin. It is pos-'sible' thus to prevent the glue from penetrating int-othewood socompletely and to retain onthe glue linea remainder suiiiciently greatto obtain a fairly good bond. However, a

large proportion of the glue still penetrates hotpress process dependson themovement of steam in a direction parallel to the'faces edges. Thechannels for the escape of steam arelargely provided by the pores of theWood which areparal'lel to theitaces of the wood.

If, however, these pores become clogged by penetration of the gluesubstance into them, then the escape of steam is seriously impeded andit may take a considerable length of time to dry the moisture from suchplywood. Besides slowing up the drying rate it makes the drying rateirregular; in some places the cells and pores will be less clogged andwill dry out faster, in other places slower. Those pores which intersectthe glue 'linewill tend to clogmore than those which do not. This leadsto crooked panels and to dih'iculties hecause of ununiformity in theirmoisture con tent. It may also lead to blisters because of excessivemoisture retained in clogged cell areas at the time the press is opened.Be-

ause of the fact that excessive heat must Y be used to dry out cloggedcell areas, this eX- cessive heat may injure the faces of the panels orcause decomposition of the wood or glue. Thus the green veneer hot platemeth- -od with wet glue has also been attended with A Process-hot press,wet veneer B Process-hot press, dry veneer C Process-cold press, dryveneer and I will show hereinafter how my new in vention may be usedwith great advantage to replace all three of these commercial processes.

I have found that many of the disadvantages of present day methods ofgluing may be eliminated by the use of a dry adhesive in the hot pressmethod, providing the process is controlled as to certain factors whichinfluence the results, both as respects the character of the adhesiveused as well as the physical conditions prevailing during the operationand when due care is used to properly control the factors which affectthe final results, very beneficial results are obtained.

The adhesive in discrete-particle form, preferably in dry powdered form,is spread on the plies. If the wood is undried containing a large art ofits original sap moisture, or is wet from lying in water, no water needbe added. If the wood be dry, water may be sprayed on the adhesive layeror the wood itself in regulated amount. The plies may then be assembledand pressed in a hot press until sufliciently dry.

The great importance of penetration of adhesive into the wood has beenshown in the preceding discussion. Penetration is the factor which mostinfluences the adhesive result obtained, so that whatever influencespenetra= tion has a direct influence on the final result.

Penetration may take place either (a) after the press is closed andpressure is applied, or (7)) before pressure is applied.

One of the reasons why dispersions have always heretofore been used ingluing, is because they are easily spread mechanically. I spreadsuspensions, employing different mechanical means than those used tospread dispersions, thereby affecting a great economy as the substancesneed have. for purposes of my invention, their particles reduced tosuspension magnitude only. \Vhile I prefer for reasons of simplicity oreconomy .to spread dry powdered adhesive basesubstances, that issuspensions in air, I am not limited to fluid suspensions in air, butmay, by the same means, spread suspensions in water or other liquidmedium, and enjoy all the benefits of using suspensions as herein setforth. In particular this may be done in the B process, or whencontrolling the moisture content of the plywood.

A point I wish to emphasize is that whereas previous gluing has beendone with dispersions, and in fact dispersions have been considered asessential to effective gluing, I.find that suspensions in air, or in aliquid have many advantages resulting in improved quality of product,besides being much more economical to use.

It will be noted that my process of control provides first a method ofcontrolling the factors so that readily dispersible substances may beused if desired and still obtain good results.

With the dispersible class of adhesives, there is no limit to the amountof water which is taken up by the adhesive, that is, if more water ispresent it mixes homogeneously with the adhesive layer and so thefluidity'keeps on increasing as long as more water is presented. In thiscase, therefore, it is more difficult to insure against excessivepenetration. Control may be exercised by previously decreasingthe amountof moisture in the wood itself so that there will not be enough presentto dilute the adhesive layer to the point where excessive penetrationresults.

Examples of dispersible adhesives that can be used with close control inmy process are animal glue or gelatin, blood albumin, soluble starchesand sodium silicate.

Examples of non-dispersible materials which may be used in certaininstances in procedures embodying the present invention are soya beanflower, other oil seed flours, seed flours generally, unconvertedstarches, gluten, and casein.

It'will be seen that penetration of adhesive must be controlled, nomatter which form of adhesion is relied upon to form the bond ('i. e.whether specific or mechanical adhesion). Either one requires that goodcontact be obtained between the glue and the surfaces to be joined andthat a good portion of the adhesive be left on the glue line when theprocess of forming the bond is completed. With dispersible adhesives-itis of particular importance that the penetration be limited.

In any method involving the simultaneous gluing and drying of greenunshrunk veneer it is obvious that the tendency of the veneer duringdrying to shrink and grow narrower transversely (that is tangentialshrinkage) will involve serious strain both'on the veneer and glue ointparticularly when in the manufacture of plywood the middle ply or coreis laid at a right angle to the faces. It is also obvious that thetendency of the veneer to grow thinner in drying (radial shrinkage)involves no such strains. Most common woods normally shrink over twiceas much tangentially as radially. The tangential shrinkage in many woodsis as much as one inch for each foot of width. Both forms of shrinkagetake place only during the removal of the last of moisture contained inthe wood. This moisture is loosely com bined with the cellulose'of thecell walls and is therefore called fibre saturation moisture. (Fibresaturation point is the maximum water thus contained in the cellulose,and averages 25% to with most woods. Free water is that contained assuch in or between the cells, over and above the fibre saturationpoint.) p

- In the A process with wet glues, means have previously been known foreliminating or neutralizing objectionable tendencies for tangentialshrinkage by the use of three stages of drying, including a finalseparate drying operation when the fibre saturation moisture is removedunder heat and pressure in presses so as to cause the wood cells tocollapse in the radial direction with beneficial densification of thewood, while the frictional resistance of .the press-plates resiststagential shrinkage. In previous practice this method of control hasbeen expensive to applyas it both involved a separate drying operationand used the hot plate press equipment as well as a dryer to perform it.Reference is made to the description of this process in U. S. Patent1,369,743, of which I was co-inventor. Under my condition of dry gluingin the A process I find that this control and elimination of shrinkageand beneficial densification of the wood may be performed all in oneoperation instead of in three, both with added efficiency and withoutany expense whatever all in the hot press, for the panels are already inthe hot press and the moisture is to be removed in any case and it istherefore simply necessary to adjust the hydraulic pressure to securethe necessary frictional resistance on the surface of the panels toprevent tangential shrinkage taking place. This results in densificationthat is radial (i. e. in a direction at right angles to theface of theplies) shrinkage,which?takestheplace oftangentialshrinkage. Aconsiderable loss of area is thereby saved, and astronger panel resultsfrom the densification. In the previous methods deficiencies in thecontrol of penetration'necessitated the use of three stages inmanufacture,

whereas my present process enables this to be done in a singleoperation.

This is a discovery of importance, as one of the most serious obstaclesto the A process hitherto has been either inabilityto satisfy thetangential shrinkage tendencies of the wood orelese the cost of applyingas a separate operation the remedy previously described. The applicationof this principle of controlling shrinkage also greatly improves thesaleability of the product besides eliminating the principal source ofspoilage.

It has a further important advantage in greatly improving the waterresistance of the glue bond, by the fact that as the bond the adhesivesubstance.

has been formed while the veneers are in the green unshrunk condition ofmaximum tangential expansion and the wood dried while in that condition,and the wood cells deformed exclusively in the direction of radialshrinkage, the tendency to a subsequent tangential movement by arewetting is eliminated. The gain in water resistance using the samequantity and kind of glue substance with the A process is frequently 50%as compared to a similar panel made from predried veneer by the B.process.

In general under my conditions of control and dry gluing newopportunities are made available for controlling and influencing thephysical character of the wood either as a whole or locally. For examplein the A process the wood may be densified and altered in structure as awhole by the previously mentioned method of resisting tangentialcollapse of the cells and inducing radial collapse during the drying outof the fibre saturation moisture in the press so that an altered wood isproduced. With cottonwood for instance I have demonstrated that panelsmade in this manner sand and stain better and are more resilient thansimilar panels not densified.

It will be noted that my process is also applicable to the gluing of dryveneer, as by.

the hot press method B process in the following way: I have indicatedbefore, the importance of the moisture content of veneer as being one ofthe factors, in fact one of the most important factors, influencingpenetration and hence the final adhesion. I have also indicated means ofcontrol of the process to secure good results when it is desired to gluegreen or wet veneer, that is, veneer where the amount of moisture is inexcess of that required by the glue substance. In this case, of course,I do not attempt to control the moisture of the veneer.

The moisture of the veneer, of course, is subject to control if myprocess is desired to be carried out by providing such control;

in other words, the veneer can be dried to any degree desired before theadhesive is applied to it in the dry state. For example, it can be drieddown'to the point where it will supply just enough moisture to theadhesive, due

, regard being had to the amount of moisture which will escape when theheat is applied.

Also, if desired, the veneer may be dried to a very low content ofmoisture, so low in fact that it cannot supply any moisture to Underthese conditions I then provide the proper amount of moisture to securethe desired fluidity in the adhesive layer by adding moisture either tothe surface of the wood to be glued or to the dry adhesive which haspreviously been spread on the surface of the wood, that is,

the dry adhesive is first spread on the dry veneer by a suitableapparatus which gives the weight of a uniform spread and then therequired amount of water is added to this dry adhesive by any meanswhich will give a uniform amount of water. The amount of water, ofcourse, which is to be added must be under control and must bepro-determined by trial, that is, it is found what amount of water bestsuits the wood and the adhesive to secure the proper conditions offluidity and penetration. The plies are then assembled and pressure andheat is applied to dry the adhesive layer and set it to a permanentbond.

For instance, I spread soya bean flour containing 13% of moisture onboiie dry veneer and after pressing obtained a bond of about 100 lbs.dry strength. It more water is added to the flour it is no longer a drypowder and it is no longer spreadable as a dry powder but by spreadingthe 13% moisture contain ing flour in the usual way and then spraying ona sufiicient amount of moisture to bring the water content up to 25% ofthe dry weight of the flour a bond of 190 lbs. dry strength wasobtained. It is therefore evident that with this wood and this adhesivea water requirement of 25% produces satisfactory results.

Under these same conditions'with bone dry wood and dry flour I obtainedequal strength by sponging or spraying on the wood an amount of waterequal to 50% of the glue, the difference in amount of water being due toa lesser amount being effectively absorbed by the glue substance underthese conditions.

This B process, it will be noted, presents also certain advantages fromthe standpoint of usin dispersible materials. In attempting to g ue wetveneer with dispersible materials the great difliculty is to preventexcessive dilution of the adhesive layer. With the above describedmodifications, however, of my process, it will be noted that just the riht amount of water may be added to disper'si 'le material so as toattain just the right condition of fluidity and hence of penetration.

For example, some modified starches are largely dispersible in water. Inattempting to glue wet veneer with such starches it is very diflicult tosecure the proper control methods to produced good commercial results.The same starches, however, when used in my modified process, whichprovides control of the moisture in the veneer or on dry veneer givesvery good results. Likewise animal glue if finely ground produces abadly starved joint with heat and green veneer, but may be made toproduce an excellent bond with heat and dry veneer. For instance, Ifound that with cottonwood and animal glue, I only obtained a bond of'GOlbs. strength with green veneer in my A process, but with dry veneer andthe sur-. faces lightly moistened in the B process liquefy under heat,it will be seen that dry adhesives have many important advantages. Forexample, blood jelly glues contain as high as seven parts of water toone of dry substance. They must have such high water content so thatthey can be spread. Comparing the action of such a jelly with my dryadhesive which may be used in this process with as little as one-quarterpart water to one part of dry substance and it will be seen that anentirely difierent case is presented as far as fluidity of adhesive andconsequent penetration is concerned and that the latter case is fareasier to control to get best results. The high moisture content of thejellied glues when used with dry veneer naturally presents seriousdifiiculties in connection with assembly time, absorption of glue waterinto the dry wood with accompanying expansion troubles, which my verylow moisture requirement avoids.

With dried blood albumen reduced to a fine powder I have produced bondsof very high strength with one-quarter part of water sprayed on the gluesubstance inmy' B process. Not only is this a reduction ofifrom to inglue water as compared to wet gluing practice, but owing to the completecontrol of penetration obtained by this method, not only are thedifiiculties connected-with penetration in wet gluing avoided but'othermeans of control of assembly-timepenetration such, for example, asaredesir able with this adhesive in my .A process may be avoided underthese conditions.

Thus by my B process I am able to produce new results impossible eitherby the prior art of wet gluing or by my A. process of dry gluing greenwood. 4

This lowering of the .water requirement b my controlled methods of drygluing is rea ily apparent in view of my conditions permitting areduction of the water requirement with a large class of glue substancesto the amount necessary to induce a moderate degree of plasticity in theglue substance as distinguished from the far greater amount required foraqueous dispersion, and obtaining proper spreading consistency.

Aqueous dispersions require from 1 parts to 7 parts of water to one ofglue substance. Sufiicient plasticity for my process is obtained with to1 parts of water and the higher amounts are only required under specialconditions where for some reason low connected with the heat isnecessary or a time value is involved. In general part of water up to anamount not substantially exceeding the weight of the adhesive meets mostconditions in the B process as contemplated by the present invention.

The advantages of my invention over the previous B process, i. e.,.dry'veneer hot press, as formerly applied using'wet glue, are:

1. Penetration is controlled.

2. Elimination of all the disadvantages preparation and spreading of thewet glue.

3. Economy of drying in the hot press, due toless water in glue. I

4. Advantages of economy of glue material, stain, and water resistance.

5. Enables minimum contact of moisture with wood, under conditions wherethis is desirable, such as very thin faces. This protection of the woodfrom injury by the glue water is accomplished by applying the waternecessary to the dry powdered glue, after the latter is spread on thewood.

Under the condition of dry gluing with vegetable proteins in both theand B processes I find that the degree of insolubility attained by theresulting bond may be greatly influenced by the' intensity of theapplication of heat during the pressing operation. For

- instance with soya bean flour containing protein I have obtained aincrease in the wet breaking strength of the bond by increasing thesteam pressure applied to the press plates from 10 lbs. to 125 lbs. andas the drying time in this instance is reduced from 120. minutes at 10lbs. pressure to 20 minutes at 125 lbs. pressure I have determined thatthe v be produced even with woods which are dif intensity of theapplication of heat is of great importance. With vegetable adhesives ingeneral I find it advantageous to use the maze imum intensity of heatavailable up to the point where injury to the product by de- Icomposition begins to take place. By so doing both the etficiency of thedrying operation and the water resistance greatly improved.

In the B processa local but very bene ficial alteration of the physicalcharacter of the wood'atfecting only a thin la er of wood liie producedcontiguous to the glue line may I by moistening thesesurfaces with thewater required to modifythe physical state of the glue substance. Thismoistening has the effect of quickly swelling the exposed fibres on thesurface. These present a greater surface therefore for the attachment ofthe glue bond and being plastic under pressure are amalgamated with theglue film as to form a very strong bond. The depth of the layer ofsoftened and swollen fibres may readily be controlled by regulating theamount and temperature of the water applied and the duraa whichappreciable expansion due to moisture tion of assembly time.

of thebond are ".cells are securely held in their final condibyspongingthe surfaces of dry cottonwood veneer with water, then spreadingwith dry soya bean flour and pressing between heated plates. When thesebonds are examined in section under the microscope, contiguous to theglue line there appears a thin layer of wood fibres completelysurrounded by and amalgamated with the dried glue substance. This layeris dense and free from voids. It is thus evident that the moistenedswollen layer of wood fibres produced by the sponging has been bothdensified by the hydraulic pressure and simultaneously penetrated by andamalgamated with the plastic glue substance while the dry wood fibres,not affected by the moisture, have not been made yielding and plastic bymoist heat and hence have been able to resist a considerable amount ofby draulic pressure without being distorted or altered. This highlydensified and amalga mated layer of wood fibres at the glue linesupplies undoubtedly in large measure the explanation of the unusuallyhigh breaking strengths noted in this process. This furficult to gluebecause under these conditions a very complete amalgamation of gluesubstances with athin layer of softened wood is thus produced and as theremoval of the fibre saturation moisture from the wood and thedehydration of the glue substance takes place simultaneously, thecollapsed wood tion by the glue substance. By controlling thetemperature and amount of Water ap lied to the wood surfaces thethickness 0 the layer of wood product can also be controlled and alsothe depth of glue penetration. The resulting plywood is flatter, stroner and better bonded than dry veneer hot plhte plywood produced byprevious methods of wet gluing as the necessity of dealingwith thelarger amountof water inherent in wet giuing, is avoided and control ofpenetration conditions and results is also much better. This method oflocal wetting of the contiguous surfaces of the plies also affords ameans of controlling the moisture of the ply as a whole so that it iskept below the point at sembly which have been so takes place. Thiseliminates danger of checking and creeping of plies during asrequiredfor satisfactory penetration.

. and since certain By my controlled methods of dry gluing many specialconditions can be met by compromises between the A and B processes.

For instance, it is often advantageous to use predried face stock andgreen unshrunk center stock and vice versa and these compromises betweenthe two methods'may be made in any degree with improved results as tocost of manufacture and character of product.

lVhile certain specific examples of modes of carrying out the inventionhave been given, it is to be understood that the invention can beutilized in a wide variety of procedures, changes may be made in theabove exemplified method without departing from the scope of theinvention, it is intended that all matter contained in the abovedescription shall be interpreted as illustrative and not in a limitingsense.

Reference is made to the following patents issued on applicationsconstituting continuations in part of the present case: Nos. 1,851,949,1,851,950, 1,851,951 1,851,952, 1,851,953, 1,851,954 and'1,851,955.

Reference isalso made to the following applications which arecontinuations in part of the present case: Serial No. 518,94A, filedFebruary 28, 1931, and Serial No; 538,983, filed May 21, 1931.

Reference is also made to the copending application of Irvin F. Laucks,Charles N. Gone and myself, Serial No. 351,822, filed April 1, 1929.

I claim:

1. The method of making plywood from wet, unshrunk plies of wood in asingle stage in a hot press without tangential shrinkage by employing adispersible adhesive base substance applied as a dry powder to saidplies, setting the limit of the penetration of said adhesive into saidplies, and applying pressure of a magnitude sufficient to preventtangential shrinkage and to densify the wood and heat of a degree to dryout the assembly.

2. The method of making plywood comprising applying to the plies anadhesive base substance in powder form dry at the time of spreading; andproviding the dry plies with a quantity of water ranging from onequarterto one and one-half (1 parts of water .to one (1) of glue substancewhich determines the penetration of the adhesive.

3. The method of making plywood, comprising applying to wet unshrunkplies an edhesive base substance in the form of a suspension in a fluidat the time of spreading; determining the degree of penetration of saidtroublesome in the Lassen;

adhesive substance into the plies by means of the adhesive being indiscrete particle form; and removing the moisture by heat while theassembly is under relatively high pressure, whereby tangential shrinkageis prevented and the wood is densified, the drying, densification andprevention of tangential shrinkage proceeding simultaneously.

4. The method of making plywood, comprising applying to wet unshrunkplies an adhesive base in powder form dry at the time of spreading;setting the limit of the degree of penetration of said adhesivesubstance into the plies; then eliminating the moisture while said pliesare subjected to pressure and heat, and substantially avoidingtangential shrinkage by subjecting the assembly to pressure inhibitiveof tangential shrinkage while the moisture is being eliminated, wherebyin a single operation a densified plywood with fiubstantially notangential shrinkage is proneed.

5. The method of making ply-wood from wet unshrunken plies of wood in asingle stage in a hot press without tangential shrinkage, by employing adispersible adhesive base substance in discrete particle form,controlling the penetration of said adhesive into said plies, andapplying pressure of a magnitude suflicient to prevent tangentialshrinkage and to densify the wood and heat of a degree to dry out theassembly.

6. A method of gluing, which comprises supplying at the glue line ablood adhesive base and a plasticizing agent in an amount substantiallyjust suflicient for the plasticization and coagulation of the adhesivematerial under bonding conditions, and subjecting to bonding conditions.7 The process of gluing, which comprises providing at the glue line ablood adhesive base and water in the proportion by weight ofapproximately four parts of adhesive material to one part of water, andsubjecting to bonding conditions.

8. The method of gluing which comprises supplying in powdered form to asurface to be incorporated an adhesive base of the character which isdispersible in cold Water, assembling and subjecting to bondingconditions the penetration being controlled without the presence ofadded materials by limiting the moisture available to substantially theamount required for the gluing.

9. The method of gluing which comprises supplying blood albumen inpowdered form to a surface to be incorporated, assembling and subjectingto bonding conditions, the penetration being controlled without thepresence of added materials by limiting the moisture available tosubstantially the amount required for the gluing.

10. The method of gluing which comprises supplying modified starch inpowdered form to a surface to be incorporated, assembling Ill andsubjecting to bonding conditions, the penetration being controlledwithout the presence of added materials b limiting the moistureavailable to substantlally the amount required for the gluing.

11. The method of making plywood, which comprises associating a dryshrunken closetextured ply with a wet unshrunken loosetextured ply, anadhesive base in discrete particle form being interposed therebetween,and subjecting to bonding conditions under pressure of amagnitudesufiicient to prevent tangential shrinkage of a wetloose-textured p 12. The method of making plywood, which comprisesassociating a dry shrunken closetextured ply with a wet unshrunkenloosetextured ply, a powdered adhesive base having been supplied to atleast one of the associated surfaces, and subjecting to bondingconditions under pressure of a ma itude suflicient to prevent tangentialshrin age of the wet loose-textured ply.

13. The method of making plywood, which comprises associating dryshrunken closetextured face plies with a wet unshrunken loose-texturedcore, a powdered adhesive base having been supplied to at least one ofeach pair of associated surfaces, and-subjecting to bonding conditionsunder pressure of a magnitude sufficient to prevent tangential shrinkageof the wet loose-textured 1y. 14. The method of making plywood, whichcomprises associating wet unshrunken loosetextured face plies with a dryshrunken closetextured core, a powdered adhesive base having beensupplied to at least one of each pair of associated surfaces, andsubjecting to bonding conditions under pressure of a magnitudesuflicient to prevent tangential shrinkage of the wet loose-texturedply.

15. The method of making plywood from a pluralitly of wood pliesincluding one or more dry shrunken plies and one or more greenunshrunken plies in the same assembly in a single stage of heattreatment, by applying an adhesive, controlling the penetration of theadhesive into the plies and simultaneously applying heat and pressure tothe assembly, the moisture in the green plies being sufficient toplasticize the adhesive, the heat being suflicient to dry out theassembly, and the pressure sufiieient to density the green plies andavoid tangential shrinkage therein.

16. The method of making plywood from moist unshrunken plies in a singlestage of heat treatment, by applying an adhesive. controlling thepenetration of the adhesive into the plies. and simultaneously applyingheat and pressure to the assembly. the heat being suflieient to dry outthe assembly. and the pressure sufficient to prevent tangentialshrinkage and density the wood.

17. The method of making plywood from dry shrunken plies, comprising thesteps of swellin a superficial layer of wood fibres on the surfaces tobe united by the application of moisture in a limited amount, a plyingdry discrete particles of an adhesive ase capable of being renderedplastic bymoisture, assembling the parts and applying pressure, wherebythe swollen wood fibres and plasticized adhesive are amalgamated to forma bond characterized by having its penetration iiinited by the depth ofthe layer of moistened res.

18. The method of making plywood from comprises providing at the glueline an adhesive base in discrete particle form and an amount of waterin a proportion by weight of approximately four parts of adhesivematerial to one part of water, and subjecting to bonding conditions.

20. The method of gluing, which comprises applying adhesive basematerial in discreteparticle form to a surface to be incorporated,supplying water in an amount not substantially exceeding 1 part of waterto 1 part of adhesive base material, and subjecting an assemblyincluding said surface to bondforming conditions.

21. The method of gluing, which comprises applying adhesive basematerial in powdered form to a surface to be incorporated, supplyingwater in an amount not substantially exceeding 1 part of water to 1 partof adhesive base material, and subjecting an assembly including saidsurface to bond-forming conditions.

22. The method of gluing, which comprises applying adhesive basematerial in powdered form to a surface to be incorporated, supplyingliquid in an amount not substantially over 1 part of liquid to 1 part ofadhesive base material, and subjecting anv assembly including saidsurface to bond-forming conditions.

23. The method ofgluing, which comprises applying animal glue inpowdered form to a surface to be incorporated, supplying water in anamount not substantially over 1 part of water to 1 part of animal glue,and subjecting an assembly including said surface to bond-formingconditions.

24. The method of gluing, which comprises applying albuminous adhesivebase material in powdered form to a surface to be incorporated,supplying water in an amount not substantially exceeding 1 part of Waterto 1 part of adhesive base material, and subjecting an assemblyincluding said surface to bond-forming conditions.

25. The method of gluing, which comprises applyingmodified starch inpowdered form THEODORE WILLIAMS DIKE.

